Amplifier circuits are used in a number of areas of electronics, for example mobile communications technology and industrial electronics.
Power amplifiers, for instance in communications technology, require amplifier stages with operating point setting. This is usually effected by feeding a quiescent current into an amplifier transistor with the aid of a current mirror or by applying a bias voltage.
FIGS. 3A and 3B show an amplifier stage that is known to the inventor and a circuit which is known to the inventor that is intended to generate a bias voltage.
FIG. 3A shows an amplifier stage having an npn bipolar transistor 7 which converts a signal U-IN to be amplified into an amplified signal U-OUT. A bias voltage for the transistor 7 is generated using a current source 4 and a further npn bipolar transistor 5.
FIG. 3B shows a circuit for generating a bias voltage with details needed to implement the current source 4 shown in FIG. 3A. The current source 4 has two pnp bipolar transistors 10, 11 and a reference current source 12. Two transistors 10, 11 which are complementary to the transistors 5, 7 are thus provided in order to implement the current source 4.
An amplifier circuit should have bias setting with a low area requirement and should therefore be capable of being implemented in a cost-effective manner. A method should make it possible to set the amplifier in a flexible manner.